Conventionally, in a mobile communication system in a WCDMA mode, a mobile station UE is configured to select a cell transmitting a downlink signal with the best quality as a serving cell through cell search procedure. The mobile station UE is configured to select only a cell transmitting a downlink signal with the best quality by the cell search.
Hereinafter, referring to FIGS. 7 and 8, description is briefly given of the cell search procedure and neighboring cell information acquisition procedure.
In FIG. 7, a receiving station receives downlink signals transmitted in cells #1 to #4 in radio base stations BTS #1 to #4 existing around the receiving cell. FIG. 8 shows an example of the receiving states of the downlink signals through the respective paths in the receiving station in this case.
Here, if the receiving station in FIG. 7 is a mobile station UE, the receiving station selects the downlink signal #3 with the best quality received via the path #3 through the cell search procedure.
However, if the receiving station performs cell search on multiple paths and acquires information on multiple neighboring cells, the receiving station can perform more advanced processing than the above.
For example, a radio base station BTS sets operational parameters in a “Plug & Play” mode, and therefore can set parameters based on a result of the cell search. Accordingly, if the receiving station shown in FIG. 7 is a radio base station BTS, the receiving station can perform more advanced processing by performing cell search on all the cells which establish the paths #1 to #4, and acquiring cell information on the cells which establish the respective paths #1 to #4.
In addition, handling of a multi-path is briefly described below referring to FIGS. 9 and 10.
In general, a mobile station UE receives a downlink signal through multiple paths from a radio base station BTS. In FIG. 9, if the paths #1 to #3 are present, the receiving states of downlink signals in a mobile station UE are shown in FIG. 10.
For the normal cell search processing to find a single cell, a radio base station BTS is configured to select only a cell which establishes a path #1 through which a downlink signal with the best quality is transmitted.
Meanwhile, when synchronization between the cell is completed, the mobile station UE can improve a communication quality by performing RAKE-combining on the downlink signals #1 to #3 with the same scrambling code which have an arrival time difference therebetween within a receiving window.
In general, such a mobile communication system employs a system design in which a same scrambling code is not assigned to neighboring cells. Further, in a case where some downlink signals are received from another cell using the same scrambling code, if the downlink signals have arrival time differences out of the receiving window, the downlink signals are not included in the RAKE-combining, and thus the downlink signals from the other cells are not combined.